President Donald Trump faces danger on multiple fronts as federal subpoenas and convictions pile up, and House Democrats dive in to scrutinize everything from his Russia dealings to his business practices, bank records, and tax returns.

But Trump’s biggest legal peril may come from offenses that, while unsexy and often overlooked, make the simplest, strongest case against him: campaign-finance violations. It was illegal campaign spending in the form of secret hush money that will soon send Trump’s ex-lawyer Michael Cohen to jail. The Trump campaign’s alleged violations range from soliciting foreign money and assistance, breaking disclosure rules, and illegally coordinating with not one but two super PACs that backed him.

The latest political money disclosures implicating Trump, however, could prove the most damaging. The Trump Inaugural Committee has faced questions for two years about how it managed to raise a record $106.7 million without properly explaining either where the money came from or how it was spent. Only $61 million of the committee’s total $103 million in expenditures has been accounted for, and reports abound of mysterious vendors with links to the Trump family, apparent above-market charges by the Trump International Hotel that point to self-dealing, and evidence of illegal foreign donations.

Now federal prosecutors in New York have subpoenaed the inaugural committee for reams of documents relating to its vendors, donors, special events, guest lists and legal or financial filings. This is serious business. Potential crimes under investigation, according to CNN, which obtained the subpoena, include donations by foreign nationals, money laundering, misreporting, pass-through donations via straw donors, false statements, and conspiracy against the United States.

Trump Inaugural Committee officials have said that all receipts and expenditures were lawful, audited and accounted for, and that they will cooperate with the investigation. But even some conservatives have flagged the inaugural committee probe as a special danger zone for Trump. The federal prosecutors investigating the inaugural, at the U.S. Attorney’s office for the Southern District of New York, are the same ones who obtained a guilty plea from Cohen on campaign-finance and other charges, including tax evasion and lying to Congress. The campaign-finance crimes, which involved payments to silence women who allegedly had affairs with Trump, directly implicated the president.

Trump has railed against House Democrats launching investigations against him, but as conservative author and commentator Andrew C. McCarthy writes in The National Review, “the more immediate threat of criminal jeopardy for the president is posed by federal prosecutors in Manhattan.” A former Chief Assistant U.S. Attorney in New York’s Southern District himself, McCarthy observes: “If I were working in the White House, my attention would not be fixed on Adam Schiff and Bob Mueller. I’d be focused on the SDNY [Southern District of New York].”

The House Intelligence Committee will also be looking into the inaugural committee’s irregular accounts, including possible foreign funding, says its chairman, California Democrat Adam Schiff. Schiff will have plenty to dig into. Political consultant W. Samuel Patton has already admitted using a straw donor to direct $50,000 to the committee from a Ukrainian politician. The committee’s chairman was Trump pal and Los Angeles investor Tom Barrack, and the finances were handled by none other than Richard Gates, lobbying partner to Trump’s jailed former campaign manager, Paul Manafort.

Both Gates and Manafort have pled guilty to conspiracy charges in connection with Special Counsel Robert Mueller’s investigation into whether the Trump campaign colluded with Russia. Among Gates’s questionable moves was reportedly to ask some vendors to accept payment directly from donors, rather than through the inaugural committee—creating an opportunity, even if inadvertently, for illegal foreign money to slip through.

Other strange dealings by the inaugural committee involve the Trump International Hotel, which may have charged above-market rates, Pro Publica has disclosed, possibly in violation of tax law. Inaugural committees operate as nonprofit entities, not campaign committees, meaning that they must observe some—but not all—of the same federal restrictions as candidates, parties, and PACs. (This is a loophole that House Democrats’ sweeping anti-corruption bill, HR 1, sets out to close.)

As early as 2017, the Campaign Legal Center and Democracy 21, two watchdog groups, complained to the Federal Election Committee that the inaugural committee’s public disclosures were riddled with inaccuracies and misrepresentations. That complaint was dismissed after the committee refiled its reports. But disclosure violations have resurfaced as a target of the federal probe. Another area ripe for investigation is the close to $26 million that the inaugural committee paid to a mysterious event-planning firm created by a friend and adviser of First Lady Melania Trump.

In the long run, the Russia collusion question looms largest over Trump, and new damning disclosures surface on that front every day. But federal prosecutors in New York may keep digging well after Mueller wraps up his probe. That means Trump could face charges if he leaves office before the statute of limitations runs out.

And even as president, Trump is not immune. While the Justice Department would probably not indict a sitting president, notes former Obama ethics czar Norman Eisen—who recently signed on to help the House Judiciary Committee with its investigation—Trump could be named an unindicted co-conspirator, as President Richard Nixon was in 1974. Politicians routinely ignore the political money rules, relying on the FEC to let things slide as usual. For Trump, though, campaign-finance violations may prove particularly hazardous in the hands of prosecutors.